24 inch mirror - 9 hrs of parabolizing

[Chanlunlun]

Dear ATMs,

After 9 hours of parabolization we finally got half way done. The mirror now has reached 50% of full correction and we are looking forward to finish rough parabolization in the coming 5 or 6 working hours.

At the moment all parabolization work was done with the 14 inch lap, ( this same lap was also used for polishing ) as the 9.5 inch parabolization lap had failed. Our strategy of parabolization is that we deliberately turn down the edge and deepen the center of mirror so that the combined effect is to force the mirror into a paraboloid shape. In this way minimum amount of glass is needed to be removed, which means that maximum labor is saved.

The Offner tester was used for the first time tonight. My first impression was that it vastly distorted the shape of the slit as viewing into the mirror. A terrible oblate spheroid with very exagerated turned up edge was observed. This is normal as when the mirror is corrected back into a flat profile ( null figure ) the figure will automatically be a paraboloid, so to speak.

The style of the Offner tester is terrible, it doesn』t look nice. As from computer simulation for maximum sensitivity the front lens of the tester has to be moved backward 322 mm from the knife edge, which introduce a very strange outlook on the equipment itself. Nevertheless the tester, in practice, was proved to be quite easy and comfortable to be handled with.

We are now quite close to the end of optical work of the 24 inch telescope. Mechanical construction work will be started in due course.

Best regards
Chan Yuk Lun
23-3-2004